Why do some pills make your eyelids heavy?

Heavy lids. The most common offenders are in the category of cold remedies and antiallergics called antihistaminics. A grat variety of them cause somnolence (sleepiness). Although there are many other medications like tranquilizers, anxiolitics (anti-anxiety), that simply depress the central nervous system and induce sleep. Thus resulting in "heavy lids". Aging of the skin too which may require lid tuck sgy.